Still looks really good to me.
Just to be curious: Is that done by cutting out one layer of foil and where more than one color is required you place another piece into the cutout?
Or is done with colored ares under the foil?
In any case I would have been a happy customer if I ordered the signs

... this is common anodized aluminium with different colours "embedded" in the oxide layer - you'll need energy densities of at least 1 Watt on a spot of 0.07mm diameter, or it won't be strong enough to "bleach" or evaporate the colour particles ...

Does somebody know how the quality, reliability and effort of this laser burning method compares to the toner transfer method? Is burning away the paint more reliable than fixating the toner to the copper? Thanks.

Quotelukie80
Does somebody know how the quality, reliability and effort of this laser burning method compares to the toner transfer method? Is burning away the paint more reliable than fixating the toner to the copper? Thanks.

... the result/quality depends on the coating material or toner and used lasers and optics.

While with laser toner transfer you can get resolutions around 600 dpi (around 43 microns pixel resolution) a good engraving laser setup can have a spot diameter of 30 microns and the smallest details can be as small as 5 microns (recalced to 850 dpi or 5000 dpi).

Another point is the needed mechanical or chemical stability of the coating - here paints or even more pre-coating with polyimide or plastic will give a much better stability/resistance ...

Quotelukier
[...] The biggest issue I have is with the paint. I've tried a few, from the cheapest black spray paint (1 GBP at one pound store) to high temperature oven & exhaust paint, to line marking paint (fast drying but ugly drying with bubbles etc) to painting a PCB with a wide tip black marker.
Pretty much every time the laser doesn't go all the way through the paint leaving a thin layer that blocks the etchant. [...]

Same problem here. Residual paint which blocks the etchant. Paint solvent is based on hydrocarbons and needs 24 hours for complete drying. I cleaned with water, soap and plastic brush. The etching result is shown in the attached photo. I used 2W power, maybe 100µm spot size, 10mm/s speed and etched 1h with Peroxydisulfate at 45°C and continuous movements.

... you need fast drying paints with pretty high loads of pigments, or a wavelength absorbing base without pigments.

Another point is the thickness of the coating - thinner works better.

When testing slow drying paints I've noticed, that the pigments evaporated instantly, but the clear polymer base could "survive" partially -- so changed to fast drying black paint used for RC cars (fuel-resitant), what worked much better ...

However, the burned paint can be removed by mechanical means by using an acrylic piece of cloth and a lot of force or by using baking soda as mechanical peeling but this takes a lot of effort. VDX, can you recommend a specific product? I had no success with my RC color brand.

By the way. I'm using a blue laser (455nm), so in contrast to IR the copper absorbs roughly 40% of laser power. So in worst case I lose 40% of the back reflected power, which results in a total power loss of 20% of my 2W. Maybe the paint does not absorb blue light as good as IR?

... I've tested different paints with NIR (975nm) and blue (445nm) diodes - all dense black paints worked -- attached an image of two of my last used paints.

One point - the IR-diode had a spot diameter of around 0.12mm, the blue of maybe 0.05mm, so I'm mostly engraving two parallel lines in 0.06mm distance with the blue diode to get a line wide enough to have a good isolation between the tracks.

Most people using the blue diodes have much bigger spot diameters (too big focussing distaces), so less energy density too -- what can be one of the problems.

I'm removing the residues in the burned tracks with a fine and pretty soft brush (hand- or tooth-brush) and warm soap water without any presure, to avoid damaging the coating ...

Thanks a lot for this valuable information! Indeed I reduced the spot size first by using a second lens very close to the PCB because I did not want to change the spot distance adjusted by my first lens (60mm). It helped a lot. I use 4 outlines spaced by 50µm.

After brushing with soap and water I also had to use a cloth soaked with gasoline to remove the burned RC paint. I have to use some pressure but the unburned paint was kept intact and the burned paint is removed nicely. Etching was also successful (Permanganate, 45°C, 20min).

(I still have to figure out the reason for the path errors visible in the picture. Gcode is fine, so it's either the firmware (backlash compensation) or the mechanics.)